Probiotics: The hidden world within you


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Beneficial bacteria present in the digestive tract play an important role in the health of the entire system. Martin Hum Ph.D, DHD, takes a look at our internal ecosystem and how replenishing these “friendly” micro-organisms can help

Your body is occupied territory. Within it is a vast population of micro-organisms that far outnumber your tissue cells. This hidden world is a complex ecosystem where over 400 species of micro-organisms co-exist, sometimes harmoniously, sometimes disruptively. When it is in balance, your internal ecosystem protects you against harmful pathogens, regulates your bowel function, and manufactures essential nutrients and enzymes.
Beneficial bacteria and harmful micro-organisms inhabit the human gut simultaneously, in a complex relationship with their host and with each other. A hundred years ago, Dr Elie Metchnikoff wrote the groundbreaking book The Prolongation of Life (Ayer & Co), in which he described this relationship as “eu-symbiosis” when beneficial to us and as “dys-symbiosis” or “dysbiosis” when it is detrimental. He postulated that toxins produced by the bacterial putrefaction of food were the root cause of degenerative illness and that the ingestion of foods fermented by lactic acid bacteria could prolong life by reducing putrefaction. Today, research has confirmed that our intestinal flora have a major impact on our health, but the mechanisms involved are more diverse and complex than Metchnikoff imagined.


The beneficial bacteria enhance our health in many ways and the list grows longer with each new piece of research. Some of their more important effects are:

Suppressing and inhibiting the growth of harmful micro-organisms, by physically crowding them out, producing natural antibiotics and lowering gut pH to levels at which most harmful bacteria fail to thrive.(1)
Manufacturing vitamin K, B-group vitamins, digestive enzymes and essential fatty acids.(2)
Digesting lactose, so preventing lactose intolerance and its associated symptoms.(3)
Enhancing the immune system, by boosting the activity of phagocytes and producing interferon-like factors.(4)
Reducing abnormally high cholesterol levels.(5)

While the internal ecosystem remains in balance, the above benefits apply and the digestion and assimilation of food and elimination of waste proceed normally. But, if things go wrong and the gut flora shift to a condition of dysbiosis, all manner of illnesses can follow. Irritable bowel syndrome, candidiasis and thrush are the most likely results of dysbiosis, but it has also been linked with inflammatory and auto-immune disorders, food allergy and intolerance, fatigue, malnutrition, neuropsychiatric symptoms and cancer.(6)

How the beneficial bowel flora can become damaged

In dysbiosis, the beneficial bacteria are overwhelmed and harmful micro-organisms proliferate. This situation is most commonly caused by the following factors:

Antibiotics kill beneficial bacteria alongside the harmful ones. Metronidazole, in particular, has been shown to trigger irritable bowel syndrome.
Steroids, non-steroidal anti-inflammatory drugs (NSAIDs), oral contraceptives, HRT and chemotherapy can disrupt the bowel flora and cause dysbiosis.
Infection by food poisoning bacteria is a common cause of dysbiosis. As we age, reduced production of stomach acid allows harmful micro-organisms to survive through to the colon.
Stress, of whatever kind, also kills off the beneficial bacteria, as well as suppressing the immune system.
A poor diet, which is low in fresh fruit and vegetables and high in processed foods, sugar, meat and dairy produce, provides the right conditions for harmful bacteria to proliferate.
Chlorinated water kills off the gut bacteria as well as the target organisms in the water supply.
Alcohol, if taken regularly in amounts of more than a glass or two a day, will also change the balance of the gut flora towards dysbiosis.


Correcting dysbiosis involves avoidance of the factors that damage the beneficial bacteria (see box on page 59), careful attention to diet and the use of anti-fungal agents and nutrients that encourage the gut mucosa to heal. But the most direct means of correcting dysbiosis is by taking supplements of the beneficial bacteria themselves, as probiotics. These powerful dietary supplements can help to re-establish a healthy balance of beneficial micro-organisms in the body. Probiotics are increasingly giving remarkable results for people with candidiasis, chronic fatigue, food sensitivities and other conditions that are often not treated effectively by conventional medicine. But not all beneficial bacteria make good probiotics. To be effective, probiotics need to:

remain viable and stable during storage and use
have no harmful side effects when taken
survive the passage through the alimentary canal, particularly the acid environment of the stomach and bile in the duodenum
establish themselves easily and multiply quickly
produce compounds that effectively suppress harmful micro-organisms.

The following bacteria have been commonly used in probiotic supplements:

Lactobacillus acidophilus

Lactobacillus acidophilus, mostly an inhabitant of the small intestine, is the best known of the lactobacilli. It has the ability to produce significant quantities of the enzyme lactase, which aids in the digestion of milk and so eliminates many of the problems associated with lactose intolerance. Lactobacilli are also responsible for the production of vitamin K, which is important in helping blood to clot and in building strong bones. Vitamin K deficiency may be a crucial factor in the onset of osteoporosis.

Dr Morton Walker, in his book Secrets of a Long Life (Devin-Adair), reports that L. acidophilus produces at least four powerful anti-microbial compounds, each of which has demonstrated neutralising effects against serious disease causing micro-organisms. Some strains of L. acidophilus are able to pass through the gut in a viable form in high concentrations.(7) Research at the University of Nebraska has shown that the DDS-1 strain of L. acidophilus, as well as having good establishment and survival characteristics, is able to reduce cholesterol levels. In laboratory studies, DDS-1 inhibited the growth and toxin producing capabilities of 23 known disease-causing pathogens, reduced tumour growth and effectively neutralised or inhibited carcinogenic substances.(8)

Lactobacillus rhamnosus

Lactobacillus rhamnosus colonises both the small and large intestine and the vagina. In part because of high levels of L. rhamnosus and other lactobacilli, the vaginal fluid is usually able to protect the body from a range of infectious diseases. L. rhamnosus strain GR-1 has been shown to colonise the urinogenital tract when used as a probiotic and to reduce the risk of subsequent infection.9 However, some other strains may fail to adhere to the vaginal or intestinal mucosa, or to survive damage from gastric acid and bile.(10)

L. rhamnosus also exhibits a number of immunological properties. In a series of studies involving children with acute rotavirus diarrhoea, L. rhamnosus strain GG shortened the duration of diarrhoea and increased the production of antibodies to the rotavirus.(11) In animal studies, L. rhamnosus has been demonstrated to increase the natural killing activity of spleen cells, which may help to prevent tumour formation. It also boosts phagocyte activity and may help the body resist microbial infections by increasing levels of immunoglobulins.

Dr Edward Brochu, of the Institute Rosell of Montreal, Canada, states that L. rhamnosus “does not only colonise, acidify and protect the small intestine, but it can quickly establish itself in the large intestine, inhibit the growth of streptococci and clostridia, create anaerobic conditions which favour the implantation of bifidobacteria and produce the biologically desirable L (+) lactic acid.”(12)

Lactobacillus salivarius

As its name suggests, L salivarius is a resident of the mouth and throat, as well as other parts of the gastro-intestinal tract. According to Scott Gregory, author of A Holistic Protocol for the Immune System (Tree of Life Publications), L. salivarius is noted for its ability to break down foods in the intestinal tract and make vital nutrients more readily available for use elsewhere in the body.

It is also claimed to support colon health by eating away encrusted putrefactive materials, and it helps repair the intestinal tract by providing needed enzymes and essential nutrients, as well as by adhering to and protecting the mucosal lining.(2)

Bifidobacterium bifidum

When a baby is born, the intestines are virtually sterile, free of micro-organisms. Immediately, friendly and harmful bacteria alike start to gain access and compete for territory and dominance. Among breast-fed babies, bifidobacteria are normally the most successful colonisers, accounting for over 90% of the gut flora. Breast-fed babies get fewer infections than formula fed ones because mother's milk tends to promote the growth of bifidobacteria in the gastro-intestinal tract, whereas replacement formulas lack this beneficial effect.

Bifidobacteria are also important in maintaining the health of the colon in adults, but their levels tend to decline dramatically as the human body ages, possibly due to changes in the acid/alkaline balance of the gastro-intestinal tract. Whereas the lactobacilli are mainly found in the small intestine, B. bifidum is more usually a resident of the large intestine.

Bifidobacterium longum

Bifidobacterium longum, another resident of the large intestine, has been found in animal studies to inhibit the formation of colon and mammary gland tumours caused by nitrosamines, found in browned or charred food. B. longum has also been shown to protect against the formation of liver tumours related to pathogenic micro-organisms in the gut.(13) Japanese research has recently shown that B. longum also produces significant amounts of B vitamins, particularly B12.2

In addition to the many kinds of resident beneficial bacteria in the body, it is constantly playing host to countless others that are just “passing through”. These include transient soil-borne organisms (SBOs)ingested with our food


In addition to the many kinds of resident beneficial bacteria in the body, it is constantly playing host to countless others that are just “passing through”. These include transient soil-borne organisms (SBOs) ingested with our food. Before the days of soil sterilisation and pre-washed vegetables, we were exposed to many more of these bacteria, some of which have remarkable therapeutic effects.

SBOs establish small colonies for brief periods of time before dying off or being flushed from the intestinal tract. However, although their presence is temporary, they contribute to the overall function and condition of the digestive system, for instance by producing by-products on which some of the most important resident beneficial bacteria depend. These two types of bacteria enjoy a complex symbiotic relationship that may dramatically influence the health and well-being of the entire body.

Because they have evolved to pass through the digestive system unscathed, SBOs are more robust and vigorous than most resident bacteria. They tolerate acid or alkaline, aerobic or anaerobic conditions and have the ability to establish temporary colonies quickly and suppress pathogenic micro-organisms effectively.(14) They can change the pH of the gut from alkaline to acidic, helping to restore the proper ratio of beneficial to harmful bacteria.

Immune system enhancement is one of the main benefits of SBOs. A study using the SBO Bacillus laterosporus has shown that it can provide relief from symptoms associated with suppressed immune system function. Another SBO, Bacillus subtilis, has also been found to boost the immune system and to stimulate the production of lymphocytes. Streptococcus thermophilis is an SBO that produces antibiotic-like substances and appears to suppress tumour development in laboratory studies.(2)


In contrast to probiotics, which are live microbial supplements, a prebiotic is a non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth of specific bacteria in the colon. Non-digestible fructo-oligosaccharides (FOS) are well established as effective prebiotics. The ingestion of 15 grams a day of FOS for 15 days by healthy volunteers has been shown to increase the bifidobacteria content of the faeces so that they are numerically predominant.(15) Several other kinds of oligosaccharides (i.e. long chain sugar molecules containing sugars other than fructose) are also being investigated as possible prebiotics, as are other substances such as lactulose, lactitol and inulin.(16)

Three criteria are required for a good prebiotic: it must not be hydrolysed or absorbed in the stomach or small intestine; it must be selective for specific beneficial bacteria in the colon; and it must induce beneficial effects in the human host. Many fruits and vegetables contain prebiotic oligosaccharides, such as onion, garlic, banana, asparagus, leek and Jerusalem artichoke. Alternatively, they can be taken as a food supplement. However, the indication that a probiotic “includes FOS”, does not mean that it contains the optimum amount to stimulate growth in the colon. Studies have shown that between 7 grams and 15 grams a day is necessary to have a significant effect.


To sum up, probiotics offer a wide range of health benefits, but it is important to buy them from a reputable company that specifies the species and strains included and the number of viable organisms per capsule (this
should be at least one billion). Preparations containing SBOs should also be considered as an adjunct to probiotic therapy and it is important to provide the right substrate for your friendly bacteria to prosper, by taking prebiotics or eating a diet containing these substances, as well.


Plummer N, Biomed Newsletter 1989:1(1).
Anon, Finding Bacteria Friendly.
Arrigoni E et al. Tolerance and absorption of lactose from milk and yoghurt during short bowel syndrome in man. Am. J. Clin. Nutr. 1994;60:926-9.
Collins J et al. Probiotic bacteria - interaction with the human immune system. In: Gut flora and health - past, present and future. (Ed. A Leeds & I Rowland), Royal Society of Medicine Press, 1996.
Anderson J & Gilliland S. Effect of fermented milk (yoghurt) containing Lactobacillus acidophilus L1 on serum cholesterol in hypercholesterolaemic humans. J. Am. Coll. Nutr.1999;18(1): 43-50.
Galland L & Barrie S. Intestinal dysbiosis and the causes of disease.
Marteau P et al. Fate and effects of some transiting micro-organisms in the human gastrointestinal tract. World Rev. Nutr. Diet 1993;74:1-21.
Shahani K, quoted in: Finding Bacteria Friendly.
Reid G et al. Urinogenital lactobacilli probiotics, reliability and regulatory issues. J.Dairy Sci. 2001; 84 (Suppl):E164-9.
Siitonen S et al. Effect of Lactobacillus GG yoghurt in prevention of antibiotic associated diarrhoea. Ann. Med. 1990;22:57-59.
Marteau P & Rambaud J-C. Therapeutic applications of probiotics in humans. In: Gut flora and health - past, present and future (Ed. A Leeds & I Rowland), Royal Society of Medicine Press, 1996.
Quoted at:
Hughes D & Hoover D, Food Technology April 1991 (Quoted in: Finding Bacteria Friendly.
Rubin R, HSOs: beyond probiotics; a natural way to boost your immune system. Healthy and Natural Journal 1998;5(5):83-86.
Gibson G & Roberfroid M. Dietary modulation of the human colonic microbiota: introducing the concept of prebiotics. J. Nutr. 1995;125:1401-12.
Crittenden R, Prebiotics. In: Probiotics: a critical review (Ed. G Tannock), Horizon Scientific Press, 1999.


Gregory S, A holistic protocol for the immune system, Tree of Life Publications, 1995.
Metchnikoff E, Prolongation of life, 1908 (Reprinted Ayer & Co 1977).
Walker M, Secrets of a long life, Devin-Adair, 1984.

Martin Hum is a registered nutritional therapist who regularly writes for nutritional magazines and is a member of the Optimum Nutrition Advisory Board.


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